1. Field of the Invention
The present invention relates to a developing method in which a latent image on a latent image support is developed by a developer support that supports a developer supplied from a developer supplier, and to a developing device, a process unit, an image forming apparatus, and an image forming method in which this developing method is employed.
2. Description of the Related Art
With a developing device of this type, if a large amount of toner (developer) is deposited on a developer supply member such as a supply roller, the pressure produced by the toner's own weight promotes aggregation of the toner, which leads to inferior image quality and various other problems. This problem has generally been dealt with by providing a second holding chamber for holding a large quantity of toner to the side of and apart from a first holding chamber for holding the developer supplier and toner, and gradually supplying the proper amount of toner from the second holding chamber to the first holding chamber, so that the aggregation of the toner is minimized around the developer supply member. Aggregation of the toner inside the second holding chamber holding a large amount of toner is minimized by stirring the toner with a rotary stirring member such as an agitator, and thereby mixing the toner with air.
Meanwhile, a so-called tandem configuration is often used in recent color image forming apparatus in order to increase the printing speed. With a tandem system, a latent image support (such as a photoconductive member) is combined with a developing device for developing a latent image supported on the surface of this support, a plurality of these combinations are lined up, and monocolor images of mutually different colors that have been developed on this photoconductive member are superposed and transferred to an intermediate transfer belt or the like. This superposed transfer forms a multicolor image (such as a full-color image). With a configuration such as this, if the combinations of latent image support and developing device are lined up horizontally, and the developing device is one in which the above-mentioned second holding chamber is disposed to the side of the first holding chamber, then a corresponding amount of space has to be left in the horizontal direction, and this ends up making the apparatus larger.
However, this increase in the size of the apparatus can be suppressed by using a taller developing device, such as the one disclosed in Japanese Laid-Open Patent Application 2001194883. This developing device has a hopper serving as a second holding chamber above a first holding chamber that encloses toner and a supply roller serving as a developer supply member. The toner in the hopper passes through a communicating passage provided between the hopper and the first holding chamber, and drops into the first holding chamber. In the first holding chamber, the supply roller, which supports toner around its peripheral face, is rotated to supply the toner on the supply roller to a developing roller serving as a developer support member. With this configuration, the second holding chamber, which takes up a particularly large amount of space in a developing device, is provided above the first holding chamber, so that the developing device has an overall shape that is taller and takes up more space in the vertical direction than in the horizontal direction, which means that the increase in space taken up in the horizontal direction can be minimized.
With a developing device with this configuration, however, a large amount of the toner that drops down from the hopper into the first holding chamber is deposited on the supply roller. The pressure produced by the toner's own weight causes the particles to aggregate, which can increase the torque of the supply roller, lead to uneven image density, or severely abrade the supply roller.
Experiments conducted by the inventors have revealed that the aggregation of toner within a tall developing device occurs most markedly between the supply roller and the opposing side wall which, out of the plurality of side walls of the first holding chamber, opposes the peripheral face of the supply roller via a relatively small gap. More specifically, with a tall configuration as with the developing device described in Japanese Laid-Open Patent Application 2001-194883, After the toner deposited on the supply roller has been supported on the surface of the supply roller, it is transported by the rotation of the roller to the supply location, which is either in contact with or across from the supply roller. Then the surface of the supply roller that has passed the supply location is advanced by its rotation back to a contact location with the deposited toner. In the space around the supply roller region, from the supply location to the contact location, if the toner should spread out laterally or move in the gravitational direction under its own weight, it will not be able to come into proper contact with the supply roller, and will end up staying where it is indefinitely. Therefore, if the above-mentioned space is ensured, this will increase the amount of wasted toner that is not used in developing.
In view of this, with a tall developing device, it is preferable for there to be as little wasted toner as possible, which is accomplished by moving the opposing side wall of the first holding chamber considerably closer to the supply roller region, from after the supply roller has passed the above-mentioned supply location up to the contact location. The developing device described in Japanese Laid-Open Patent Application 2001-194883 and the tall developing device used in the experiments conducted by the inventors both had this configuration.
Nevertheless, with this configuration, if toner that has dropped down from the hopper into the first holding chamber and been deposited on the supply roller is subjected to higher pressure due to the increase in the deposited amount, or is pressed against the toner in the hopper, it may work its way in between the supply roller and the opposing side wall of the first holding chamber. This toner that has worked its way in can bind movement within this small space, and is difficult to dislodge from the gap. Meanwhile, toner deposited on the supply roller readily works its way into this gap, so the pressure of the toner in the gap steadily builds, until the toner finally becomes an aggregated block. When this aggregated block presses against the supply roller, it raises the torque of the supply roller, increases image density unevenness, and leads to abrasion of the supply roller.
A toner that contains wax in its particles has often been used in recent years in an effort to achieve oilless fixing OR low-temperature fixing, but such toner is relatively soft, and the adhesion between particles is relatively strong, so this toner is prone to forming an aggregated block, which makes the problems mentioned above more likely to occur.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Laid-Open Patent Applications S60-218679, H10-020640, H10-039612, and H11-167282.